*{
    margin: 0;
    padding: 0;
    user-select: none;
    transition: all 500ms,font 0s;
}
html{
    overflow-x: hidden;
}
body{
    display: block;
    max-height: 100vh;
}
.ul{
    position:fixed;
    background-color: rgb(54, 54, 54);
    height: 50px;
    width: 100vw;
    border-bottom: 2px solid rgb(97, 97, 97);
    border-radius: 0 0 0 8px;
    z-index: 100;
}
.ul li{
    list-style: none;
    float: left;
    text-align: center;

}
.ul li a{
    display: block;
    padding: 14px 18px;
    text-decoration: none;
    color: aliceblue;
    font-weight: bold;
}
.ul .li_home{
    margin-left: 100px;
}
.ul li a:hover {
    background-color: rgb(180, 180, 180);
    color: rgb(43, 43, 43);
}
.ul .li_user{
    float: right;
    background-color: rgb(54, 54, 54);
    border-left: 2px solid rgb(54, 54, 54);
    border-right: 2px solid rgb(54, 54, 54);
    width: 150px;
    height: 50px;
    margin-right: 100px;
}
.ul .li_user img{
    border: 3px solid rgb(151, 150, 150);
    border-radius: 5px;
    width: 40px;
    height: 40px;
}
.div_user{
    position: absolute;
    background-color: rgb(54, 54, 54);
    display: block;
    width: 150px;
    top: 50px;
    right: 100px;
    border-bottom: 2px solid rgb(97, 97, 97);
    border-left: 2px solid rgb(97, 97, 97);
    border-right: 2px solid rgb(97, 97, 97);
    border-radius: 0 0 8px 8px;
    overflow: hidden;
    z-index: -1;
    transform: translateY(-160px);
    transition: all 250ms;
}
.div_user .username{
    font-weight: bolder;
    padding: 15px 0;
    color: aliceblue;
    border-bottom: 2px solid rgb(97, 97, 97);
}
.ul .li_user .div_user a{
    font-weight:500;
}
.ul .li_user:hover .div_user{
    transform:translateY(0);
}
.main{
    position: relative;
    display: flex;
    top: 150px;
    left: -50px;
    height: auto;
    justify-content: center;
    margin-bottom: 280px;
}
.book{
    position: relative;
    background-color: rgb(250, 241, 217);
    width: 1129px;
    height: 1800px;
}
.comment{
    position: relative;
    background-color: rgb(176, 176, 177);
    top: -59px;
    left: 80px;
    width: 600px;
    height: 1888px;
}
.tail{
    position: absolute;
    width: 100vw;
    height: 100px;
    background-image: url(../img/tail.png);
    background-size: 8%;
    text-align: center;
}
.tail p{
    position: relative;
    color: aliceblue;
    font-weight: bold;
    top: 25px;
}